When a pedestrian collides with a vehicle, a head or the like of the pedestrian collides with a hood or windshield of the vehicle. This results in serious injury. In particular, since a substantial member such as an engine existing under the hood may bring about a large injury, an invention of lifting the hood or a technology of disposing an airbag on the hood is proposed for protecting the pedestrian or decreasing the injury.
However, these mechanisms protecting the pedestrian should not be always operated, so that it is expected that these mechanisms be operated only when a collision object is determined to be a pedestrian. For instance, in adopting these mechanisms, various adverse influences result from operating a protecting device on the hood (e.g., active hood) when a collision object is not a pedestrian. When a light object that collides with a vehicle, such as a triangle corn or a signboard indicating road construction, cannot be discriminated from a pedestrian, the protecting device is uselessly operated. This involves useless repair costs. Further, by contrast, when a heavy stationary object that collides with a vehicle, such as a concrete wall or another vehicle, cannot be discriminated from a pedestrian, a problem occurs that the hood being lifted is backed into an interior of the vehicle, harming an occupant of the vehicle.
Accurately determining whether a collision object is a pedestrian is thereby more required than before, so that several methods for determining the collision object are proposed. For instance, Patent document 1 proposes a collision object determining technology using an electrostatic capacitance. Here, a difference in electrostatic capacitance is electrically detected between a pedestrian and a collision object that is a conducting member (including a resistance member in this specification), based on variations of electrostatic capacitance between the collision object and an electrode plate of an electrostatic capacitance sensor. Patent document 2 proposes a technology using a load sensor (or collision load sensor) that detects impact. Here, a kind of the collision object is determined based on variations of a collision load waveform that is detected by the load sensor.
(Patent document 1: JP-2000-326808 A)
(Patent document 2 JP-H11-028994 A)
The collision object determining technology using an electrostatic capacitance has an advantage in detecting a pedestrian before a collision to thereby enable a sufficient period for dealing with the collision. However, this technology has a disadvantage. Namely, a difference in the electrostatic capacitance between a pedestrian (human body) and a metal member is small; further, inclination in the sensor output has the same direction. Discriminating a person from metal thereby sometimes becomes difficult, depending on kinds or shapes of the metal. Further, to detect the electrostatic capacitance between a pedestrian and an electrode plate disposed in the vehicle, the capacitance is varied based on a positional relationship between the pedestrian and electrode plate in a vehicle-width direction (or in a side to side direction of the vehicle). Accurately determining that a pedestrian actually collides with the vehicle is thereby not easy, so that a problem occurs that the pedestrian protecting device starts to operate even when no pedestrian collides with the vehicle. For instance, even when a person touches a bumper or passes very close to the bumper, the collision with the pedestrian is mistakenly determined to thereby cause the pedestrian protecting device to operate.
Next, the technology using the collision load sensor has an advantage in accurately detecting a collision, but has a disadvantage in needing a quick response for dealing with the collision since the collision is detected after the collision actually occurs. Further, the collision load sensor is difficult to discriminate a person from a collision object having a mass, rigidity, and a friction coefficient with a road, that resemble those of a person. A problem thereby occurs that it is difficult to discriminate a person from a signboard or fence that has a weight resembling that of a person.
Namely, each of the pedestrian determining technology using the electrostatic capacitance and the pedestrian determining technology using the collision load sensor has the disadvantage in decreasing accuracy in determining the collision object.